1. The keyboard you're using right now
Your keyboard can be an incredibly accurate representation of what's in your nose and your stomach. Of 33 randomly sampled computer keyboards tested by a British consumer group this year, four were dirty enough to be considered a health hazard, and one harbored hundreds of times more bacteria than your average toilet seat. Of course, not everyone's keyboard is this dirty; contributing factors include not washing your hands after using the bathroom, picking your nose, and eating at your computer (especially at work), as the crumbs left behind tend to become little bacteria factories. Experts recommend regularly swabbing your keyboard with lightly-dampened alcohol wipes on a regular basis -- and be sure to shake those cookie crumbs out, too.
2. The kitchen
The way some folks keep their kitchens, it would be more sanitary to prepare dinner in the bathroom. You wouldn't know they were a health hazard to look at them, but everything from chopping boards and dishcloths to the plastic washing-up bowls they use in the UK and elsewhere can -- and often do -- harbor an immense amount of food-borne bacteria. Put them all together -- knives and a chopping board used to prepare raw chicken or fish in a plastic tub with warm soapy water -- and you have almost ideal conditions for the spread of bacteria. Add to that the dishcloth you dry every dish with, which hangs semi-damp over the lip of the sink when not in use, and you've got a real kitchen nightmare (as opposed to the Gordon Ramsey kind). The solution? Health experts recommend washing up in the sink itself instead of a plastic tub, washing the sink out with bleach regularly, changing those dishtowels regularly and, ideally, installing a sensor-activated faucet so dirty hands aren't always touching the tap handles.
3. Men's wallets
Of the everyday items in your house, one of the most fertile breeding grounds for bacteria is a man's wallet. You touch everything in it regularly -- as do whatever strangers have passed its contents on to you -- and it stays in your back pocket, a nice warm place for bugs to breed. (Proximity to one's booty was not otherwise considered a factor.) But are wallets a more serious menace than salmonella-encrusted kitchen sinks? Researchers at the International Scientific Forum on Home Hygiene say no: "It is not whether bacteria are present, or how many there are, but what type they are."
4. Women's desks
Sorry, ladies. It seems your desks -- at home and at work -- are often up to 400 times more bacteria-laden than a toilet seat, and 3 to 4 moreso than a man's desk. A research team at the University of Arizona offered several explanations: first and foremost, that women are more likely to keep snacks in their desk drawers, which promote mold and incubate bacteria like nobody's business. Secondly, make-up and lotions aid the transfer of bacteria from surface to surface, and more frequent contact with small children -- who, let's face it, can be pretty germy -- was also a contributor. "If there's ever a famine," one of the researchers said, "the first place I'll look for food is a woman's desk."